Surely you must be joking. There have been Explorer bugs that went unpatched for six months. No operating system is immune and security flaws arising from bugs in code are an inevitable accompaniment to having code in the first place, especially complex code with lots of moving parts (some of them infrequently tested/visited), but Microsoft has historically been Macrosquishy when it comes to security and patches. LOTS of holes, and many of them (in the historical past) have taken a truly absurd amount of time to be patched, resulting in truly monumental penetration of trojans and viruses via superrating wounds like Outlook. I still get an average of one email message a day that makes it through my filters purporting to be from a correctly named friend or a relative and encouraging me to click on a misspelled link. You think those messages are arising from successful data-scraping via Linux malware or Apple malware or FreeBSD malware?
Perhaps, driven by the need to actually compete with Apple and Linux (including Android) instead of resting on their monopolistic laurels, they have cleaned up their act somewhat over the last few releases of Windows, but on average over the last 10 or 15 years, certainly since the widespread adoption of apt and yum to auto-maintain Linux, the mean lifetime of a security hole in a Linux based system all the way out to user desktops has been around 24 hours -- a few hours to patch it and push it to the master distro servers, mirror it, and pull it with the next update. Microsoft hasn't even been able to acknowledge that a bug exists on that kind of time frame, let alone find the problem in the code, fix it, test it, and push it.
If they are doing better now, good for them! However, look at the relative penetration of malware even today. Linux malware has a very hard time getting any sort of traction. Apple malware has a very hard time getting any sort of traction. Windows? It's all too easy to whine that it gets penetrated all the time because it is so popular and ubiquitous, except that nowadays it is neither.
rgb